A wide variety of implantable medical devices (IMDs) that deliver a therapy or monitor a physiologic condition of a patient have been clinically implanted or proposed for clinical implantation in patients. In some instances, IMDs may provide the capability to monitor a physiological condition of a patient, such as pressure, electrocardiogram (ECG), oxygen level or the like. In such cases the IMDs may or may not provide therapy to the patient. If therapy is delivered to the patient in addition to monitoring the physiological condiction, the IMDs may include a therapy module that delivers therapy to a variety of organs, nerves, muscles or tissues of the patients, such as the heart, brain, stomach, spinal cord, pelvic floor, or the like. In some cases, IMDs may deliver electrical stimulation therapy via one or more electrodes, which may be included as part of one or more elongated implantable medical leads.
For example, an implantable cardiac device, such as a cardiac pacemaker or implantable cardioverter-defibrillator, provides therapeutic stimulation to the heart by delivering electrical therapy signals such as pulses or shocks for pacing, cardioversion, defibrillation or cardiac resynchronization via electrodes of one or more implantable leads. As another example, a neurostimulator may deliver electrical therapy signals, such as pulses, to a spinal cord, brain, pelvic floor or the like to alleviate pain or treat symptoms of any of a number of neurological or other diseases, such as epilepsy, gastroparesis, Alzheimer's, depression, obesity, incontinence and the like.
IMDs may also deliver, in addition to or instead of electrical stimulation therapy, drug therapy. For example, the IMD may deliver a drug or other therapeutic agent to the patient to treat pain or other symptoms of the condition of the patient. For example, the IMD may deliver morphine to an intrathecal location to treat pain. As another example, the IMD may deliver chemotherapy for the treatment of cancer. An IMD that delivers a drug or other therapeutic agent may sometimes be referred to as a drug pump or drug delivery device.
IMDs include a telemetry module that may exchange communications with a programming device (sometimes referred to as a programmer). For example, the IMDs may transmit information related to a condition of a patient, such as physiological signals measured by one or more sensors, or information related to a therapy delivered to the patient. This information may be previously stored or real-time information. The IMDs may also receive information from the programmer, such as configuration information that may be used to configure a therapy to be provided to the patient.
The various components of the IMDs, including the therapy module and the telemetry module, receive power from a power source. The power source may, in some instances, be a battery that has a limited service life. The service life of the battery may vary greatly based on the type of therapy provided to the patient. The service life of the battery, however, is typically on the order of several to tens of years.
To extend the life of the power source, the various components may periodically power up to perform a function and power down when not performing a function. The various components periodically power up and power down in accordance with a timer, such as a crystal oscillator. For example, a telemetry module may periodically power up in accordance with the timer to transmit or receive communications. As another example, a sensing module may periodically wake up based on the timer to sense a physiological signal of the patient.